There is a nascent class of robots—so called “soft” robots—that contain no (or few) rigid internal structural elements, and are loosely modeled on animals with non-rigid body parts (starfish, squid, and others). Many of these soft robots are actuated pneumatically using gas transferred to them from a stationary source via a flexible tether. The limitations imposed by size are one primary reason that they have been designed to function with compressed gas supplied through an external pneumatic tether. Although this tether may interfere with some tasks, it is often an advantage rather than a disadvantage for others: for example, it enables the transfer or sampling of fluids and solids and facilitates electronic communication and optical observation.
Many soft robots rely on compressed air that is introduced through a tether from a source of compressed air, e.g., a pressurized cylinder or other pressurized gas source. The robot is limited in its mobility by the length and number of tethers. In addition, the tethers can add significant weight required for the soft robot to move along with it, as it perambulates. Other attempts at on-board power source include chemical pumps or other chemical systems that generate gas on site on the soft robot.
Robots intended for use outside of laboratory environments should be able to operate without the constraints of a tether; this is especially true for robots intended to perform demanding tasks in challenging environments (for example, for search and rescue applications in unstable rubble).